In highly integrated circuits nowadays the packing density achieved is so great that it becomes difficult to provide the circuit casing with the required number of "terminal legs".
For instance, at present integrated circuits are being used which comprise a great number of (internal) different functional groups of which only selected ones, however, are to be active during normal operation. The desired functional group at present is activated by external circuitry associated with individual "terminal legs". This external circuitry may be embodied by fixed wiring by means of which certain terminals are placed at certain potentials (logical 0 or logical 1). Instead of fixed wiring also mechanical or electrical switches may be used.
A reduction of the required number of "terminal legs" is obtained by applying coded signals to the control terminals for the selection of certain structural groups. The signals may be binary coded and the integrated circuit in that event comprises an internal decoder. In this manner two possibilities of selection may be realized by a number n of terminal legs.